The present invention relates to a copier, facsimile apparatus, printer or similar image forming apparatus and more particularly to an improved cover member enclosing a plurality of developing sections arranged on a revolver type developing unit.
It is a common practice with a full-color copier or similar full-color image forming apparatus to sequentially expose an image carrier to image light representative of images of different separated colors to thereby form latent images. The latent images are developed by toner of colors complementary to the color-separated light to turn out toner images. The toner images are sequentially transferred to a paper or similar recording medium one above the other, forming a full-color image. A multicolor image forming apparatus sequentially exposes an image carrier to images to be reproduced in different colors and thereby sequentially forms latent images. These latent images each are developed by a developer of particular color. The resulting toner images are sequentially transferred to a paper one above the other. This type of image forming apparatus, whether it be full-color or multicolor, needs a plurality of developing devices for developing latent images in different colors. The problem with such developing devices is that they increase the overall size of the apparatus when constructed independently of each other and arranged around the image carrier.
In light of the above, a revolver type developing unit having a plurality of developing sections arranged on a rotary body has been proposed in various forms in the past. The rotary body is positioned in the vicinity of an image carrier. The developing unit is rotatable to bring any one of the developing sections to a developing position for developing a latent image formed on the image carrier with toner stored in the developing section.
For example, Japanese Patent Publication No. 4-23782 and Japanese Patent Laid-Open Publication No. 4-29166 each disclose an image forming apparatus constructed to replace the entire revolver type developing unit when any one of the developing sections reaches a toner end condition. This kind of apparatus has a problem that even a developing section holding a sufficient amount of toner must be discarded, wasting the toner and thereby increasing the running cost. For example, the images of ordinary documents are mostly output in black and white. The ratio of images output in black and white to images output in color is generally understood to be 9:1 to 7:3. This means that black toner is consumed far more than toner of colors other than black, and therefore much of the toner of colors other than black is simply wasted. Further, because the developing unit is replaced as soon as a toner end condition occurs, even members not reached the end of life must be discarded. Moreover, a system and facilities for collecting, disassembling and recycling the developing unit made up of various materials are essential and increase the initial cost and running cost.
Japanese Utility Model Laid-Open Publication No. 4-38362 proposes an image forming apparatus including a revolver type developing unit storing black toner in a greater amount than toner of colors other than black. This kind of apparatus reduces the waste of toner of colors other than black and therefore reduces the increase of the running cost, compared to the apparatuses of the above Publication No. 4-23782 and Laid-Open Publication No. 4-29166. Even this apparatus, however, cannot fully obviate the waste of toner because the amount of consumption depends on the toner. In addition, the apparatus, like the apparatuses of the above documents, increases the substantial initial cost and running cost.
Japanese Patent Laid-Open Publication No. 61-97674 and Japanese Patent Publication No. 6-5403 each disclose an image forming apparatus including a plurality of toner cartridges fixedly mounted on the body of the apparatus and each storing toner of particular color therein. The toner cartridges each are connected to a particular developing section of a revolver type developing unit by a flexible tube. A toner conveyor member is disposed in each flexible tube and caused to rotate in accordance with the consumption of the associated toner so as to replenish fresh toner to the associated developing section. However, the prerequisite with this configuration is that the flexible tubes and toner conveyor members must be prevented from twisting. The apparatus, therefore, needs a connecting section for selectively interrupting the connection between the developing sections and the tubes in accordance with the condition of rotation of the developing unit. In addition, the connecting section must be provided with shutters and seal members for preventing toner from flying about and leaking and preventing toner of different colors form being mixed. As a result, the apparatus needs a complicated construction including a great number of parts, resulting in an increase in initial cost.
Japanese Patent Publication NO. 7-43551 teaches an image forming apparatus including toner replenishing means arranged at one end of a revolver type developing unit and a slider slidably supporting the developing unit. This kind of apparatus is capable of replenishing toner of particular color to each developing section without resorting to the above connecting section. The apparatus, however, must have the parts of the developing unit to be cleaned, inspected, adjusted and replaced and must, when use is made of a two-ingredient type developer, have the carrier of the developer periodically replaced. That is, the operator has not only to replenish toner but also to maintain the developing unit periodically. The above slider is used to facilitate such maintenance work. However, the slider has a complicated and rigid configuration and thereby increases the initial cost of the body of the apparatus. Moreover, the developing unit must be bodily replaced when the life of any one of the developing sections expires, noticeably increasing the running cost. Black toner, for example, is consumed far more than toner of colors other than black, as stated earlier. It follows that the developing section storing black toner is used far more frequency than the other developing sections. Therefore, if all the developing section have the same durability, then the developing section storing black toner reaches the end of life earlier than the other developing sections. This requires the developing section storing black toner to have high reliability and high maintenance ability.
Japanese Patent Laid-open Publication Nos. 60-208779, 61-73163 and 61-103175 each propose an image forming apparatus in which the developing sections of a revolver type developing unit are implemented as cartridges or magazines disposable independently of each other. In this apparatus, only if the developing unit is rotated to bring desired one of the cartridges or magazines to a preselected position for replacement, it can be removed from the apparatus, as shown and described in, e.g., the above Laid-Open Publication Nos. 60-208779 and 61-103175. However, the miniaturization and cost reduction of the developing unit available with this apparatus are limited because each developing section needs respective end walls and casing and because a particular support member must be assigned to each developing section. Moreover, the operator must maintain the developing sections one by one, resulting in time- and labor-consuming work. For example, the developing sections storing toner other than black toner are used at substantially the same rate and usually reach the end of life almost at the same time, although the amount of consumption depends on the toner. Such developing sections are, in many cases, replaced at the same time.
Japanese Patent Publication No. 59-26954, Japanese Patent Laid-Open Publication Nos. 60-233669, 6-85266 and 62-102261, Japanese Utility Model Laid-Open Publication No. 63-26847 and Japanese Patent Laid-Open Publication No. 63-41871 each disclose an image forming apparatus constructed to miniaturize the revolver type developing unit and therefore the entire apparatus and to output black-and-white images stably with high quality. This apparatus includes an exclusive black developing unit for development in black and a revolver type developing unit (simply revolver hereinafter) arranged in the vicinity of a photoconductive element or image carrier. The black developing unit stores black toner. The revolver is rotatable to bring any one of its developing sections to a preselected developing position. The operator is capable of handling the black developing unit used more frequently than the developing sections of the revolver independently of the revolver type developing unit. This facilitates the maintenance of the black developing unit. However, some different problems are apt to occur, depending on the configuration of each of the two developing units. For example, the apparatus taught in the above Laid-Open Publication No. 60-233669 needs particular end plates and a particular casing for each of the three developing sections arranged thereon, and a particular support plate for each of the three developing sections. This limits the miniaturization and cost reduction of the revolver. In addition, handling the three developing sections one by one results in time- and labor-consuming maintenance work.
To solve the above problems, Japanese Patent Laid-Open Publication No. 9-114179 discloses an image forming apparatus including a cartridge storing black toner and a revolver having developing sections storing toner of colors different from black. Toner of particular color is replenished to each of the developing sections of the revolver in accordance with the consumption of toner. With this apparatus, it is possible to facilitate the manipulation of the cartridge assigned to black and used more often than the revolver and the manipulation of the revolver in which each toner is consumed in a particular amount. Further, a toner replenishing device is located at one end of the revolver and conveys toner in the axial direction of the rotary shaft of the revolver. This miniaturizes the revolver and toner replenishing device and enhances the free layout of the inside of the apparatus. However, the apparatus lacks a member for protecting the periphery of the revolver. It is therefore likely that the developing rollers of the revolver are scratched when the cartridge storing black toner is mounted and dismounted from the apparatus. Further, toner is apt to fly out of the developing units and contaminate the inside of the apparatus. In addition, black toner is apt to fly out of the cartridge and be mixed with toner stored in the revolver.
Japanese Patent Laid-Open Publication No. 10-177298 teaches an image forming apparatus including a hollow cylindrical cover member surrounding a revolver and formed with an opening facing a developing position where an image carrier is present. Handles are provided on the cover member such that they can be retracted to closely contact the circumference of the cover member. The cover member is a solution to the problem of the above Laid-Open Publication No. 9-114179.
However, if the mechanical strength of the above cover member is short, then the cover member is apt to deform when the black developing unit contacts the cover member and exerts a force thereon during mounting or dismounting. The deformation of the cover member is likely to damage developing rollers and other members arranged in the revolver. Further, when the cover member is implemented by, e.g., a molding of resin, it is apt to bend, distort or otherwise deform during molding or machining. This also brings about damage to the structural parts of the revolver and causes toner on the developing rollers to fly about.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 6-332285, 63-146077 and 2-287577, and Japanese Utility Model Laid-Open Publication No. 1-135448.